hildren of low-income and minority families have high prevalence of early childhood caries. Since they have much better access to medical care and social services than to dental care, we propose to implement a program to apply fluoride varnish (FV), a low cost, low tech caries prevention agent, to the teeth of lowncome 1-3 year olds in community-based primary care centers (CPCCs) and in California Special Supplemental Nutrition Programs for Women, Infants and Children (WIC). We will use a stratified 2x2 factorial (4-arm) cluster-randomized controlled practical clinical trial of 48 sites testing: (1) FV delivery on-site (OSFV) or referring to a dentist for FV (RFV) and (2) telephone counseling systems (proactive outgoing calls or passive receptive toll-free calls) on caries incidence and increment, and on reach of FV preventive treatment in 1-3 year olds. Strata are CPCC or WICs. Six consenting sites will be enrolled in each stratum in each of Years 1-4 for a total of 24 sites/stratum. Sites within each stratum will be randomly assigned either to the OSFV or the RFV Group. Sites within each Group will be randomly assigned either to a proactive or passive automated telephone format for the provision of culturally sensitive, linguistically concordant caregiver counseling for the prevention of ECC. A sub-sample of 60 consenting child-caregiver dyads will be recruited from each site in all 4 arms of each stratum. The 1-3 year old child will receive a baseline and12-mo follow-up clinical dental exam. Digital images of all teeth will be transmitted off site for assessment by a calibrated dentist blinded to group assignment to determine caries. At 12 mo postbaseline, providers at each site will complete a follow-up questionnaire and a random sample of all caregivers of eligible 1-3 year olds from each site will receive follow-up automated phone callsand to determine if their child received FV. After the 12 mo follow-up, the sites assigned to the RFV group will be offered training to switch to an OSFV group. All groups will be followed for another 6 mo to assess reach and sustainability under more real world conditions. In year 5, Year 1 sites will be evaluated for program sustainability using qualitative interview measures. Sites in each arm within and between strata will be compared for reach of FV exposure among all eligible 1-3 year olds, for caregiver engagement with the counseling formats, and for program adoption, fidelity, cost, and sustainability across client populations.